Adhesives are mainly classified into a solvent type adhesive and a aqueous emulsion type adhesive. Of these, the solvent type adhesive has disadvantages such that the use thereof involves problems such as ignition or fire due to a used solvent and health and environment problems such as environmental pollution. On the contrary, the aqueous emulsion type adhesive has no problem such as above.
Aqueous emulsion type adhesives are comprised of fine water-insoluble resin particles with particle sizes of 0.05 to 10 .mu.m and dispersed in water as a medium. To disperse the resin particles in water, it is necessary to allow an aqueous component to exist on the particle surface. The method for allowing the aqueous component to exist includes adsorption of a surfactant and copolymerization of an aqueous comonomer. When such an aqueous emulsion type adhesive is used, however, the surfactant or aqueous component remains in the formed adhesive coating or is present largely in the interface of the coating, leading to deterioration in coating strength or strength adhered to material. Specifically, low-polar plastic resin films tend to be hardly adhered. Photographic materials, which are generally provided with a sublayer to perform adhesion between a plastic resin film support such as a polyester and a light-sensitive layer, are processed with a developer at a high pH or heated to form images, so that when applying the aqueous emulsion type adhesive described above to the sublayer, it is needed to have adhesion sufficient for such an image forming treatment with a developer or by heating and therefore, an adhesive with higher adhesion is desired.
Attempts to enhance adhesion of the aqueous emulsion type adhesive include a technique of using an emulsion without using a low molecular weight surfactant, for example, JP-A 5-287248 discloses a technique of using polyvinyl alcohol as a protective colloid and as a adhesive, a latex comprised of copolymer of ethylene, vinyl acetate and acetoacetic acid allyl ester (herein, the term, JP-A means an unexamined and published Japanese Patent Application). However, as a sublayer of the photographic material which is to be subjected to the processing described above is insufficient the adhesion. JP-A 63-218952 discloses a technique of incorporating a polymer latex containing an active methylene group into a sublayer of a polyester support. In this technique, its adhesion property is exhibited to a certain extent, but when subjected to recent rapid processing or an image forming treatment by heating, sufficient adhesion was not obtained. Toku-hyo-hei (PCT Application Publication) No. 8-503687 discloses an aqueous coating composition comprised of a copolymer of vinyl acetate and dialkyl maleate, which is polymerized in a polyester containing a sulfonic acid group and a polymer containing an active methylene group. When this polymer mixture composition is applied to photographic materials, however, sufficient adhesion was not obtained after subjected to an image forming treatment by developing or heating.